What Causes Strep Throat?

To anyone who might know.. I was diganosed with strep throat but did not get test, my doctor believed that because my right lymph node was swollen in the front that it was strep. it has been 3 days now on antibiotics and i still feel awful. No sore throat but still having a fever, stomach pain, no appetite,joints hurting, and super tired. I also just had Strep B less then 2 week ago, and take macrobid once a day which has been going on for about 2 months now for urinary issues. How could I get strep? please help!